1. Field of the Invention
This invention relates to a radiation imaging apparatus, wherein an imaging operation is performed by use of an array of a plurality of radiation detector units, each of which is provided with a solid-state radiation detector, wherein image composing processing is performed on image signals, each of which is outputted from one of the radiation detector units, and in accordance with the array of the plurality of the radiation detector units, and wherein a composed image signal is thereby acquired.
2. Description of the Related Art
With respect to X-ray (radiation) imaging operations for medical diagnoses, and the like, various X-ray imaging apparatuses, in which solid-state radiation detectors (utilizing semiconductors as principal sections) are utilized as X-ray image information recording means, have heretofore been proposed and used in practice. With each of the X-ray imaging apparatuses described above, X-rays carrying image information of an object is detected by the solid-state radiation detector, and an image signal representing an X-ray image of the object is thereby obtained.
As for the solid-state radiation detectors to be utilized in the X-ray imaging apparatuses, various types of solid-state radiation detectors have heretofore been proposed. For example, from the view point of an electric charge forming process for converting the X-rays into electric charges, the solid-state radiation detectors may be classified into a photo conversion type of solid-state radiation detector and a direct conversion type of solid-state radiation detector. With the photo conversion type of the solid-state radiation detector, fluorescence, which has been produced by a fluorescent substance when X-rays have been irradiated to the fluorescent substance, is detected by a photo-conductor layer, and signal electric charges having thus been generated in the photo-conductor layer are accumulated at a charge accumulating section. Also, the signal electric charges having thus been accumulated at the charge accumulating section are converted into an image signal (an electric signal), and the thus obtained image signal is outputted from the solid-state radiation detector. With the direct conversion type of the solid-state radiation detector, signal electric charges, which have been generated in a photo-conductor layer when the X-rays have been irradiated to the photo-conductor layer, are collected with a charge collecting electrode and accumulated at a charge accumulating section, the signal electric charges having thus been accumulated at the charge accumulating section are converted into an electric signal, and the thus obtained electric signal is outputted from the solid-state radiation detector. In the direct conversion type of the solid-state radiation detector, the photo-conductor layer and the charge collecting electrode constitute a principal section.
Also, from the view point of an electric charge read-out process for reading out the accumulated electric charges to the exterior, the solid-state radiation detectors may be classified into an optical read-out type of solid-state radiation detector and a thin-film transistor (TFT) read-out type of solid-state radiation detector. With the optical read-out type of the solid-state radiation detector, reading light (a reading electromagnetic wave) is irradiated to the solid-state radiation detector, and electric charges having been accumulated are thereby read out. With the TFT read-out type of the solid-state radiation detector, TFT's connected to a charge accumulating section are actuated successively, and electric charges having been accumulated are thereby read out. (The TFT read-out type of the solid-state radiation detector is described in, for example, U.S. Pat. No. 6,828,539.)
The applicant proposed an improved direct conversion type of solid-state radiation detector in, for example, U.S. Pat. No. 6,268,614. The improved direct conversion type of the solid-state radiation detector is a direct conversion type and optical read-out type of a solid-state radiation detector. The improved direct conversion type of the solid-state radiation detector comprises a recording photo-conductor layer, which is capable of exhibiting photo- conductivity when recording light (the X-rays, the fluorescence produced through irradiation of the X-rays, or the like) is irradiated to the recording photo-conductor layer. The improved direct conversion type of the solid-state radiation detector also comprises a charge transporting layer, which acts approximately as an electrical insulator with respect to electric charges having a polarity identical with the polarity of latent image charges, and which acts approximately as an electrical conductor with respect to transported electric charges having a polarity opposite to the polarity of the latent image charges. The improved direct conversion type of the solid-state radiation detector further comprises a reading photo-conductor layer, which is capable of exhibiting the photo-conductivity when a reading electromagnetic wave is irradiated to the reading photo-conductor layer. The recording photo-conductor layer, the charge transporting layer, and the reading photo-conductor layer are overlaid in this order. The signal electric charges (i.e., the latent image charges) carrying image information are accumulated at an interface (i.e., a charge accumulating section) between the recording photo-conductor layer and the charge transporting layer. Also, electrodes (i.e., a first electrical conductor layer and a second electrical conductor layer) are formed on opposite sides of the combination of the three layers described above. In the improved direct conversion type of the solid-state radiation detector, the recording photo-conductor layer, the charge transporting layer, and the reading photo-conductor layer constitute a principal section.
Further, there have heretofore been proposed various radiation detecting cassettes (i.e., radiation detector units) comprising a case housing, in which a solid-state radiation detector, an electric power source, and the like, are accommodated. (A radiation detecting cassette is described in, for example, U.S. Pat. No. 5,661,309.) The radiation detecting cassettes are comparatively thin and have a size enabling conveyance. Therefore, with the radiation detecting cassettes, imaging operations are capable of being performed with a high flexibility. For example, with respect to a patient who is not capable of moving, it is possible to perform the imaging operation, wherein the patient is allowed to lie down on a bed, the radiation detecting cassette is located under a site, the image of which is to be recorded, and a radiation source of a radiation imaging apparatus is moved to a position above the patient, which position stands facing the radiation detecting cassette. Also, the radiation detecting cassette is capable of being loaded into an imaging apparatus, such as a mamma image recording and read-out apparatus, and an imaging operation is capable of being performed in this state.
In the field of the radiation imaging, it is often desired that the imaging operation is capable of being performed on an object having a markedly large area as in the cases of general vertebral column imaging operation, general lower extremity imaging operation, or the like. However, in cases where the imaging operation on the object having a markedly large area is to be performed by use of the radiation detecting cassette, the imaging range is not capable of being covered with one radiation detecting cassette. Therefore, in such cases, it may be considered that the imaging operation is performed by use of a plurality of radiation detecting cassettes, which are arrayed in a one-dimensional direction or two-dimensional directions, and that the image signals having been outputted from the plurality of the radiation detecting cassettes are combined with one another in accordance with the array of the radiation detecting cassettes.
However, ordinarily, the solid-state radiation detector is not capable of being located over the entire area of a radiation irradiation surface of each of the radiation detecting cassettes. Therefore, in cases where the imaging operation is to be performed by use of the plurality of the radiation detecting cassettes arrayed in the manner described above, if the plurality of the radiation detecting cassettes are arrayed on an identical plane, the image information corresponding to joint sections of the radiation detecting cassettes will not be capable of being acquired. Accordingly, it is necessary that the radiation detecting cassettes are located at different distances from the radiation source, such that end regions of adjacent radiation detecting cassettes may overlap each other, and such that all of the image information corresponding to the imaging range may be capable of being acquired.
However, if the radiation detecting cassettes are located at different distances from the radiation source, the image size of the obtained object image will vary for different radiation detecting cassettes, and an image will not be capable of being composed accurately.